Chilean Blue Whales Research Articles

Chilean blue whales off Isla Grande de Chiloe, 2004-2010: distribution, site-fidelity and behaviour

A collaborative research program (the Alfaguara Project) has collected information on Chilean blue whales (Balaenoptera musculus) off Isla Grande de Chiloe, in southern Chile, through eight aerial and 85 marine surveys. A total of 363 individual blue whales was photo-identified from 2004 to 2010. Approximately 20% of all catalogued individuals were resighted within the same season and 31% were resighted between years. Recaptures of photo-identified individuals from other areas to the north and south of the main study area support the hypothesis that the feeding ground off southern Chile is extensive and dynamic. The high overall annual return and sighting rates highlight the waters off northwestern Isla de Chiloe and northern Los Lagos as the most important aggregation areas currently known for this species in Chile and one of the largest in the Southern Hemisphere. Observations on feeding and social behaviour also were recorded. These results provide important information on the conservation status of Chilean blue whales and highlight the necessity that long-term photographic identification research and line-transect surveys to monitor health conditions and population trends be continued off northwestern Isla de Chiloe. The high frequency of large vessels in the mouth of the Chacao Channel (along the north side of Isla de Chiloe) and the high number of blue whales in the area raises the possibility of vessel collisions. Therefore, it is necessary to develop and implement a conservation plan for these whales to address this and other potential threats.

Seasonal Trends and Diel Patterns of Downsweep and SEP Calls in Chilean Blue Whales

To learn more about the occurrence and behaviour of a recently discovered population of blue whales, passive acoustic data were collected between January 2012 and April 2013 in the Chiloense ecoregion of southern Chile. Automatic detectors and manual auditing were used to detect blue whale songs (SEP calls) and D calls, which were then analysed to gain insights into temporal calling patterns. We found that D call rates were extremely low during winter (June–August) but gradually increased in spring and summer, decreasing again later during fall. SEP calls were absent for most winter and spring months (July–November) but increased in summer and fall, peaking between March and April. Thus, our results support previous studies documenting the austral summer residency of blue whales in this region, while suggesting that some individuals stay longer, highlighting the importance of this area as a blue whale habitat. We also investigated the daily occurrence of each call type and found that D calls occurred more frequently during dusk and night hours compared to dawn and day periods, whereas SEP calls did not show any significant diel patterns. Overall, these findings help to understand the occurrence and behaviour of endangered Chilean blue whales, enhancing our ability to develop conservation strategies in this important Southern Hemisphere habitat.

Seasonal Occurrence of Sympatric Blue Whale Subspecies: the Chilean and Southeast Indian Ocean Pygmy Blue Whales With the Antarctic Blue Whale

There are multiple blue whale acoustic populations found across the Southern Hemisphere. The different subspecies of blue whales feed in separate areas, but during their migration to lower-latitude breeding areas each year, Antarctic blue whales become sympatric with pygmy and Chilean blue whales. Few studies have compared the degree of this overlap of the Southern Hemisphere blue whale subspecies across ocean basins during their migration. Using up to 16 years of acoustic data, this study compares the broad seasonal presence of Antarctic blue whales, Chilean blue whales, and Southeast Indian Ocean (SEIO) pygmy blue whales across the Pacific and Indian Oceans. Antarctic blue whales were sympatric with the other two blue whale subspecies during the migrating season of every year. Despite this overlap, Chilean and pygmy blue whale detections peaked earlier during the austral autumn (April–May) while Antarctic blue whale detections peaked later during the austral winter (June). Chilean (Pacific Ocean) and SEIO (Indian Ocean) pygmy blue whales showed similar seasonal patterns in detections despite occurring in different ocean basins. Though we have shown that Antarctic blue whales have the potential to encounter other blue whale subspecies during the breeding season, these distinct groups have remained acoustically stable through time. Further understanding of where these whales migrate will enable a better insight as to how these subspecies continue to remain separate.

Body size data collected non-invasively from drone images indicate a morphologically distinct Chilean blue whale (Balaenoptera musculus) taxon

The blue whaleBalaenoptera musculus(Linnaeus, 1758) was the target of intense commercial whaling in the 20thcentury, and current populations remain drastically below pre-whaling abundances. Reducing uncertainty in subspecific taxonomy would enable targeted conservation strategies for the recovery of unique intraspecific diversity. Currently, there are 2 named blue whale subspecies in the temperate to polar Southern Hemisphere: the Antarctic blue whaleB. m. intermediaand the pygmy blue whaleB. m. brevicauda. These subspecies have distinct morphologies, genetics, and acoustics. In 2019, the Society for Marine Mammalogy’s Committee on Taxonomy agreed that evidence supports a third (and presently unnamed) subspecies of Southern Hemisphere blue whale subspecies, the Chilean blue whale. Whaling data indicate that the Chilean blue whale is intermediate in body length between pygmy and Antarctic blue whales. We collected body size data from blue whales in the Gulfo Corcovado, Chile, during the austral summers of 2015 and 2017 using aerial photogrammetry from a remotely controlled drone to test the hypothesis that the Chilean blue whale is morphologically distinct from other Southern Hemisphere blue whale subspecies. We found the Chilean whale to be morphologically intermediate in both overall body length and relative tail length, thereby joining other diverse data in supporting the Chilean blue whale as a unique subspecific taxon. Additional photogrammetry studies of Antarctic, pygmy, and Chilean blue whales will help examine unique morphological variation within this species of conservation concern. To our knowledge, this is the first non-invasive small drone study to test a hypothesis for systematic biology.

Seasonal acoustic presence of blue, fin, and minke whales off the Juan Fernández Archipelago, Chile (2007–2016)

The southeast Pacific (SEP) contains the home ranges of several migratory large whale species, determined largely based on research in coastal waters. These whales’ pelagic seasonal residency is unknown. The Juan Fernandez Archipelago (JFA) is an offshore island in the SEP where passive acoustic monitoring (PAM) data collection is ongoing at the HA03 hydroacoustic station (sample rate of 250 Hz) maintained by the Preparatory Comprehensive Nuclear-Test-Ban Treaty Organization. Six years (2007–2009 and 2014–2016) of PAM data from HA03 were examined for the acoustic presence of Antarctic, Chilean (southeast Pacific 1, southeast Pacific 2), and southeast Indian Ocean blue whale song types; the fin whale 20-Hz song; and minke whale vocalizations. The weekly presence or absence of these six vocalization types was annotated manually by an expert analyst and then averaged across all years. For each vocalization type, the number of weeks per month with presence was averaged over all years. Consistently, we found austral wintertime presence of Antarctic blue, fin, and minke whales; and the year-round presence of Chilean blue whales. Southeast Indian Ocean blue whales were also detected, but very rarely. We discuss the possible seasonal movements of each species or acoustic group in the offshore SEP. This is the first year-round multispecies study of baleen whale in the offshore SEP and provides valuable information for understanding the migrations of endangered baleen whales in this region, highlighting the importance of offshore areas as hotspots for baleen whale biodiversity.

Morphometric analysis of Chilean blue whales and implications for their taxonomy

AbstractIn the Southern Hemisphere, blue whales are currently divided into two subspecies, Antarctic blue whales (Balaenoptera musculus intermedia) and pygmy blue whales (B. m. brevicauda), but there is some debate about whether Chilean blue whales should also be considered as a separate subspecies. Here, we provide novel morphometric data to directly address this taxonomic question from a biological survey of 60 blue whales taken during the 1965/1966 Chilean whaling season. The data show that maximum body length and mean body length of both sexually mature females and males for Chilean blue whales are intermediate between pygmy and Antarctic blue whales; and that fluke‐anus lengths of Chilean blue whales are significantly different from pygmy blue whales, but not necessarily from Antarctic blue whales. There is also some support from the data that snout‐eye measurements are different among all three groups. These data provide further confirmation that Chilean blue whales are a distinct population requiring separate management from other blue whale populations, and are also consistent with suggestions that Chilean blue whales are not the same subspecies as pygmy blue whales.

First assessment of persistent organic pollutant contamination in blubber of Chilean blue whales from Isla de Chiloé, southern Chile

Persistent organic pollutants (POPs) were assessed for the first time in blue whales from the South Pacific Ocean. Concentrations of polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs), hexachlorobenzene (HCB) and dichlorodiphenyltrichloroethane and its main metabolites (DDTs), were determined in 40 blubber samples from 36 free-ranging individuals and one stranded, dead animal along the coast of southern Chile between 2011 and 2013. PCBs were the most abundant pollutants (2.97–975 ng/g l.w.), followed by DDTs (3.50–537 ng/g l.w.), HCB (nd–77.5 ng/g l.w.) and PBDEs (nd–33.4 ng/g l.w). There was evidence of differences between sexes, with lower loads in females potentially due to pollutants passing to calves. POP concentrations were higher in specimens sampled in 2013; yet, between-year differences were only statistically significant for HCB and PBDEs. Lower chlorinated (penta > tetra > tri) and brominated (tetra > tri) congeners were the most prevalent among PCBs and PBDEs, respectively, mostly in agreement with findings previously reported in blue and other baleen whales. The present study provides evidence of lower levels of contamination by POPs in eastern South Pacific blue whales in comparison to those reported for the Northern Hemisphere.

From Chilean Patagonia to Galapagos, Ecuador: novel insights on blue whale migratory pathways along the Eastern South Pacific.

BackgroundThe most traditional scheme for migration among baleen whales comprises yearly migrations between productive waters at high latitude summer feeding grounds and warmer waters at lower latitudes where whales calve and mate, but rarely feed. Evidence indicates, however, that large departures from this scheme exist among populations and individuals. Furthermore, for some populations there is virtually no information on migratory pathways and destinations. Such is the case of Chilean blue whales throughout the Eastern South Pacific; hence, the goal of this study was to assess its migratory behavior.MethodsDedicated marine surveys and satellite tagging efforts were undertaken during the austral summer and early autumn on blue whale feeding grounds off Chilean Northern Patagonia (CNP) during 2013, 2015 and 2016. Positional data derived from satellite tags regarding movement patterns and behavior were analyzed using Bayesian switching first-difference correlated random walk models.ResultsWe instrumented 10 CNP blue whales with satellite transmitters and documented individual variation in departure time, northbound migratory routes and potential wintering grounds. The onset of migration occurred from mid/late austral autumn to well into the austral winter. Blue whales moved in various directions, but ultimately converged toward a general NW movement direction along a wide corridor exceeding 2,000 km. Area-Restricted Search behavior was exhibited within fjords and channels of CNP and also South of Galapagos Archipelago (GA) and northern Peru, but never during migration. Interestingly, dive profiles for one whale that reached GA showed a sharp and consistent increase in depth north of 5°S and extreme deep dives of up to 330 m.DiscussionInformation derived from satellite tagged blue whales in this study is the first of its kind off the Eastern Southern Pacific. Our results provide valuable information on their migratory timing, routes and behavior on their northbound migration, particularly regarding the varied migratory plasticity for this particular population. Our results also highlight the first record of two complete migratory paths between CNP and GA and strengthen the hypothesis that GA waters correspond to a potential wintering destination for CNP blue whales. We further hypothesize that this area might be selected because of its biological productivity, which could provide feeding opportunities during the breeding season. Our results suggest that special efforts should be put forward to identify blue whale critical areas and understand key behavioral aspects in order to provide the basis for their conservation on a regional context (i.e., reducing potential ship strike and promote Marine Protected Area (MPA) implementation in Chile, Ecuador and Peru). Indeed, we suggest joint blue whale conservation efforts at the regional level in order to identify and determine potential threats and impacts and, most importantly, implement prospective management actions.

Estimates of Abundance and Trend of Chilean Blue Whales off Isla de Chiloé, Chile

Since 1970, blue whales (Balaenoptera musculus) have been seen feeding in the waters off southern Chile during the summer and autumn (December to May). Investigation of the genetic, acoustic and morphological characteristics of these blue whales shows that they are a distinct but unnamed subspecies, called the Chilean blue whales. Photo-identification surveys have been conducted in the waters off northwestern Isla Grande de Chiloé, southern Chile from 2004–2012 and Isla Chañaral, central Chile in 2012. Over this time, 1,070 blue whales were encountered yielding, after photo-quality control, 318 and 267 unique photographs of the left and right side of the flank respectively. Using mark-recapture analysis of left and right side photographs collected from Isla Grande de Chiloé (2004–2012), open population models estimate that ~570–760 whales are feeding seasonally in this region. POPAN superpopulation abundance estimates for the same feeding ground in 2012 are 762 (95% confidence intervals, CI = 638–933) and 570 (95% CI 475–705) for left and right side datasets respectively, very similar to results from closed population models. Estimates of trend revealed strong variation in abundance, peaking in 2009 and [suggesting] fluctuating use in the survey area over time, likely related to the density of their prey. High inter-annual return rates suggest a degree of site-fidelity of individuals to Isla Grande de Chiloé and that the number of whales using this feeding ground is relatively small.

Genetic variation in blue whales in the eastern pacific: implication for taxonomy and use of common wintering grounds.

Many aspects of blue whale biology are poorly understood. Some of the gaps in our knowledge, such as those regarding their basic taxonomy and seasonal movements, directly affect our ability to monitor and manage blue whale populations. As a step towards filling in some of these gaps, microsatellite and mtDNA sequence analyses were conducted on blue whale samples from the Southern Hemisphere, the eastern tropical Pacific (ETP) and the northeast Pacific. The results indicate that the ETP is differentially used by blue whales from the northern and southern eastern Pacific, with the former showing stronger affinity to the region off Central America known as the Costa Rican Dome, and the latter favouring the waters of Peru and Ecuador. Although the pattern of genetic variation throughout the Southern Hemisphere is compatible with the recently proposed subspecies status of Chilean blue whales, some discrepancies remain between catch lengths and lengths from aerial photography, and not all blue whales in Chilean waters can be assumed to be of this type. Also, the range of the proposed Chilean subspecies, which extends to the Galapagos region of the ETP, at least seasonally, perhaps should include the Costa Rican Dome and the eastern North Pacific as well.

Blue whale population structure along the eastern South Pacific Ocean: evidence of more than one population.

Blue whales (Balaenoptera musculus) were among the most intensively exploited species of whales in the world. As a consequence of this intense exploitation, blue whale sightings off the coast of Chile were uncommon by the end of the 20th century. In 2004, a feeding and nursing ground was reported in southern Chile (SCh). With the aim to investigate the genetic identity and relationship of these Chilean blue whales to those in other Southern Hemisphere areas, 60 biopsy samples were collected from blue whales in SCh between 2003 and 2009. These samples were genotyped at seven microsatellite loci and the mitochondrial control region was sequenced, allowing us to identify 52 individuals. To investigate the genetic identity of this suspected remnant population, we compared these 52 individuals to blue whales from Antarctica (ANT, n = 96), Northern Chile (NCh, n = 19) and the eastern tropical Pacific (ETP, n = 31). No significant differentiation in haplotype frequencies (mtDNA) or among genotypes (nDNA) was found between SCh, NCh and ETP, while significant differences were found between those three areas and Antarctica for both the mitochondrial and microsatellite analyses. Our results suggest at least two breeding population units or subspecies exist, which is also supported by other lines of evidence such as morphometrics and acoustics. The lack of differences detected between SCh/NCh/ETP areas supports the hypothesis that eastern South Pacific blue whales are using the ETP area as a possible breeding area. Considering the small population sizes previously reported for the SCh area, additional conservation measures and monitoring of this population should be developed and prioritized.

High genetic diversity in a small population: the case of Chilean blue whales.

It is generally assumed that species with low population sizes have lower genetic diversities than larger populations and vice versa. However, this would not be the case for long-lived species with long generation times, and which populations have declined due to anthropogenic effects, such as the blue whale (Balaenoptera musculus). This species was intensively decimated globally to near extinction during the 20th century. Along the Chilean coast, it is estimated that at least 4288 blue whales were hunted from an apparently pre-exploitation population size (k) of a maximum of 6200 individuals (Southeastern Pacific). Thus, here, we describe the mtDNA (control region) and nDNA (microsatellites) diversities of the Chilean blue whale aggregation site in order to verify the expectation of low genetic diversity in small populations. We then compare our findings with other blue whale aggregations in the Southern Hemisphere. Interestingly, although the estimated population size is small compared with the pre-whaling era, there is still considerable genetic diversity, even after the population crash, both in mitochondrial (N = 46) and nuclear (N = 52) markers (Hd = 0.890 and Ho = 0.692, respectively). Our results suggest that this diversity could be a consequence of the long generation times and the relatively short period of time elapsed since the end of whaling, which has been observed in other heavily-exploited whale populations. The genetic variability of blue whales on their southern Chile feeding grounds was similar to that found in other Southern Hemisphere blue whale feeding grounds. Our phylogenetic analysis of mtDNA haplotypes does not show extensive differentiation of populations among Southern Hemisphere blue whale feeding grounds. The present study suggests that although levels of genetic diversity are frequently used as estimators of population health, these parameters depend on the biology of the species and should be taken into account in a monitoring framework study to obtain a more complete picture of the conservation status of a population.

Chilean Blue Whales as a Case Study to Illustrate Methods to Estimate Abundance and Evaluate Conservation Status of Rare Species

Often abundance of rare species cannot be estimated with conventional design-based methods, so we illustrate with a population of blue whales (Balaenoptera musculus) a spatial model-based method to estimate abundance. We analyzed data from line-transect surveys of blue whales off the coast of Chile, where the population was hunted to low levels. Field protocols allowed deviation from planned track lines to collect identification photographs and tissue samples for genetic analyses, which resulted in an ad hoc sampling design with increased effort in areas of higher densities. Thus, we used spatial modeling methods to estimate abundance. Spatial models are increasingly being used to analyze data from surveys of marine, aquatic, and terrestrial species, but estimation of uncertainty from such models is often problematic. We developed a new, broadly applicable variance estimator that showed there were likely 303 whales (95% CI 176-625) in the study area. The survey did not span the whales' entire range, so this is a minimum estimate. We estimated current minimum abundance relative to pre-exploitation abundance (i.e., status) with a population dynamics model that incorporated our minimum abundance estimate, likely population growth rates from a meta-analysis of rates of increase in large baleen whales, and two alternative assumptions about historic catches. From this model, we estimated that the population was at a minimum of 16.5% (95% CI 7.3-34.4%) of pre-exploitation levels in 1998 under one catch assumption and 12.4% (CI 5.4-26.3%) of pre-exploitation levels under the other. Thus, although Chilean blue whales are probably still at a small fraction of pre-exploitation abundance, even these minimum abundance estimates demonstrate that their status is better than that of Antarctic blue whales, which are still <1% of pre-exploitation population size. We anticipate our methods will be broadly applicable in aquatic and terrestrial surveys for rarely encountered species, especially when the surveys are intended to maximize encounter rates and estimate abundance.

Preliminary recordings of blue whale (Balaenoptera musculus) vocalizations in the Gulf of Corcovado, northern Patagonia, Chile

Sound production in many great whale species is thought to function as communication between individuals (Evans 1967, Cummings and Thompson 1971, as reviewed in Tyack 2000), and is often related to feeding and mating behavior (Croll and Tershy 2002, Oleson et al. 2007a). The sounds generally associated with blue whales (Balaenoptera musculus) are lowfrequency (mainly below 80 Hz) high-intensity calls around 188 dB re 1-Pa (rms) that travel over long distances in the ocean environment, (e.g., Cummings and Thompson 1971, Sirovic et al. 2007). The only previous study of blue whales in Chilean waters was conducted by Cummings and Thompson (1971). They reported a three-part call characteristic of the species; however, the higher precursory pulses have rarely appeared in the literature, possibly due to the limitation of many instruments in capturing higher sounds. Recently, off California, McDonald et al. (2001) reported a “high-frequency precursory component to the B call” near 400 Hz, which “shows significant variation in character [. . .] and may be analogous to a 390 Hz component which preceded the last call segment in recordings of Chilean blue whales.” A song can be made up of various such call units repeated in a distinctive patterned sequence, which appear to display important geographical variation (Stafford et al. 2001). Thus sequences from the north Atlantic (Mellinger and Clark 2003), the southeast Pacific (Cummings and Thompson 1971), the eastern tropical Pacific (Stafford et al. 1999), the northeast Pacific (e.g., Thompson et al. 1996, Stafford

SEPARATING SOUTHERN BLUE WHALE SUBSPECIES BASED ON LENGTH FREQUENCIES OF SEXUALLY MATURE FEMALES

AbstractWhen sexually mature, Antarctic (true) blue whales are substantially longer than pygmy blue whales. To estimate the proportions of these two subspecies in various regions, Bayesian mixture models were fitted to catch length frequencies of sexually mature females. The extent of rounding to 5‐ft intervals was also estimated. Antarctic blue whales dominated (99.2%) pelagic catches south of 52°S, whereas pygmy blue whales dominated (99.9%) north of 52°S and in 35°–180°E. South of 60°S, only 0.7% (95% credibility interval 0.5%–1.0%) were pygmy blue whales, lower than the 7% upper bound currently assumed. Shore‐based catches from SW Africa and those before 1937 from South Georgia and the South Shetlands were estimated to contain 90%–92% Antarctic blue whales. Actual proportions were probably higher, but these data show evidence of rounding (up to 19% of records), poor length‐estimation methods, and other problems. The mean length of sexually mature female Chilean blue whales (77.1 ft, 23.5 m) was intermediate between pygmy (68.9 ft, 21.0 m) and Antarctic blue whales (83.4–86.3 ft, 25.4–26.6 m). A good fit to these data was obtained only by assuming that the Chilean whales are a separate subspecies or distinctive population. This finding is also consistent with their discrete distribution, and genetic and call type differences, compared to Antarctic and pygmy blue whales.